The present invention relates to a process for preparing a laminated resin product having a high oil resistance, gas-barrier properties and high mechanical strength which comprises a substrate made of a polyester, a polyamide or a hydrolyzed copolymer of ethylene-vinylacetate.
Polyesters, polyamides, and hydrolyzed copolymers of ethylene-vinylacetate (hereinafter referred to as hydrolyzed EVA) have high gas barrier properties, oil resistance and high strength. However, they are relatively hard to use in the food and automobile fields alone because of their high cost and high steam permeability. On the other hand, polyolefins have been used in various fields because of low cost, high mechanical strength, transparency, moldability and sanitary properties. However, polyolefins have inferior gas-barrier properties and oil resistance and, accordingly, when polyolefins are used as food containers for mayonnaise or soybean sauce, a long storage life of the food is not attained. When polyolefins are used as gasoline containers, the gasoline is lost by permeation and the container is deformed by swelling, disadvantageously. In order to overcome the disadvantages of polyolefins, various improvements have been proposed, however, a satisfactory result has not been attained because of complicated processes, high cost and limitation of usage and design.
As one improvement, it has been proposed to form a laminated sheet with a polyester, a polyamide, a hydrolyzed EVA, etc. which has characteristics to overcome said disadvantages.
However, polyolefins are nonpolar materials as is evident from their chemical structure, and they have low affinity for said resins. Accordingly, even though a polyolefin is melt pressed with one of said resins, the layers of the laminated product can be easily removed by peeling.
It has been proposed to provide an adhesive composition layer between the layers of said resins. However, it is necessary to have an additional step of coating an adhesive composition in said case whereby the lamination process is disadvantageously complicated.